Gas masks, respirators or other respiratory protection systems using permanent or replaceable cartridges and/or canisters are commonly used for protection against a variety of airborne pollutants. Respirator cartridges/canisters usually contain one particulate filter for toxic or nontoxic materials (“particulate filter”) and a sorption media for adsorption or absorption of gases and vapor content in the atmosphere. While these devices provide excellent protection against hazardous materials, there capacity to provide protection is limited and may be depleted with use, exposure to chemicals, or fouling. Therefore, for the cartridge and/or canister to provide effective of protection of the user the cartridge/canister must be replaced prior to the end of its service life.
The cartridges/canisters should be changed prior to the end of their operational life span. However, predicting the life span of the filter cartridges/canisters is complicated task. The sorption capacity of the sorbent is dependent on parameters such as relative humidity, ambient temperature, the concentration and specific properties of the contaminant(s) absorbed by the sorption media and the volume and rate of air passing through the cartridge/canister.
Contemporary safety practice requires all gas respirators to have a reliable method for indication of the end of their service life. If a direct measurement method is not practical, a schedule of cartridge use and replacement thereby tracking the exposure should be implemented. The use of replacement schedules, even most advanced ones, requires reliance on historical monitoring of the working environment, estimation of the average total exposure and approximation of the results according to measured or predicted theoretical capacity of the cartridge under certain circumstances. Not only do the surrounding environmental conditions contribute to the total load on the sorption media of the respirator, but also the volume of air that has passed through the media needs to be determined to calculate the load and the end of service life of the cartridge/canister. The respiration capacity of the different users and the changes of this capacity under different environmental and (light or heavy) working condition could lead to big (up to 3-4 folds) differences in the total load in the same well monitored environmental conditions. The cartridge of one worker may reach its end of service life more quickly than another worker even under the same environmental conditions. Further, the same person performing the same work under different temperature and humidity levels may show sufficient differences in respired volume. To track many cartridges under different conditions, times and working places is very complicated and sometime even impossible task. These are considered to be drawbacks of the accepted scheduling methods for determining end of service life. Therefore, a variety of methods and devices attempting to provide real monitoring and end of service life estimating using the exposure concentration, exposure time and total air flow through the sorbent have been developed.
There are a variety of methods and devices designed to indicate the depletion or end of service life of the sorption layer (sorption bed) in the gas canisters/cartridges for respirators. Depletion of the sorption layer is dependent on the industrially generated different volatiles (organic or inorganic) in the air which must be cleaned up according to required safety standards. The vapor pressure of the volatile's varying in very big range and their ability to get sorbed on the sorption bed is inversely proportional to the volatility—the less volatile substance with small vapor pressure has better sorption and the sorbent shows higher capacity to them. As the sorption capacity for a particular substance defines the moment of breakthrough, for every substance this moment is different, therefore real time monitoring of the depletion of the sorbent is preferred.
One direct method involves sensors with a change of the color of sorbent along the sorption bed (BG Pat. 31666 to Mihaylov) or color change in the indicating material placed along the sorbent bed inside of transparent wall “of additional indicating cartridge in flow after the main filter cartridge” Australia Pat. WO9,512,432 or on the wall inside of the filter cartridge U.S. Pat. No. 6,497,756 B1 and U.S. Pat. No. 4,326,514. Such material indicates irreversible changes in the sorption bed after being saturated by certain dangerous material. Drawbacks of these types of sensors are their narrow specificity which limits their use to specific needs and well known situations for expected substances and gas mixtures, mainly for inorganic gases and vapors as in U.S. Pat. No. 4,326,514; U.S. Pat. No. 4,873,970, U.S. Pat. No. 5,323,774 and U.S. Pat. No. 6,497,756.
Leichnitz in U.S. Pat. No. 4,684,380 teaches a colorimetric sensor for toxic gases. The sensing element comprises a granulated material, similar to one used in detector tubes, immobilized between two screens and is transparent to the gas flow. The placement of such sensor on the back of the sorption layer is observable through a lens in the back of the cartridge. A similar colorimetric approach is used in U.S. Pat. No. 5,297,544 where array of indicator means with a plurality of indicating ranges are used. They are forming chip-like support element with indicating colorimetric indicator portions exposed to air being inhaled. Such means are situated between outer full piece mask and inner half-mask. The indicator different ranges are used for visual examination or optical evaluation with appropriate means. In U.S. Pat. No. 5,666,949 such colorimetric sensors are combined with an electronic reading system. Despite the electronic reading system, the sensor is actually a colorimetric one. The drawbacks of the colorimetric sensors are defined by their (before mentioned) specificity. The colorimetric type sensors are humidity (RH) and temperature (T) dependent which are important parameters for all chemical colorimetric reactions.
Another direction of real time end of service life indicator is using electronic temperature sensor situated immediately after the sorption bed as in U.S. Pat. No. 4,440,162 to Sewel at all. This sensor, however, is limited and usable only for substances presented at high concentration and having a large temperature effect when absorbed on the sorption media. These sensors are, therefore, not widely applicable. Saturation process at low concentration for long period of time can cause breakthrough and pass undetected.
Recent approach for end-of-service-life indication are some active type ESLI's. They comprise electronic components to monitor the level of contaminants and a visual or audible signal to provide an automated warning to the user. Some historical attempts are described in U.S. Pat. No. 3,902,485; U.S. Pat. No. 3,911,413, both never been implemented because of bulkiness, high cost and low sensitivity. In 1978 NIOSH selected a metal oxide sensor (MOGS) to act as service life indicator for organic vapor air purifying respirators. This sensor was chosen on the basis of low cost, commercial availability and its desirable non specific behavior to large variety of organic vapors. The main drawback of MOGS is the large current drain caused by relatively high operational temperature (˜200 C). Two patents, U.S. Pat. No. 4,873,970 and U.S. Pat. No. 4,847,594, describe a standard electrochemical measuring cell. The proposed warning cartridge was designed to fit in between the facemask and respirator cartridge. A drawback of this design is that toxic gases could only be detected once the breakthrough already occurs, therefore the system may not comply with NIOSH recommendation for adequate warning 20-25% before 100% of the cartridge is depleted. U.S. Pat. No. 5,512,882 advantageously suggest a generic sensor inside of the cartridge adsorbent. Similar approach had U.S. Pat. No. 5,018,518. U.S. Pat. No. 5,297,544 is teaching the indicator that simultaneously registered the retention effect of the filter and the sealing effect of the edge of the mask. Furthermore this patent proposed the use of a miniaturized computer chip-like indicator system capable of detecting pollutants at different levels. The indicator system itself was anticipated to consist of a light source and detector. The light intensity, measured as reflected or transmitted light, was a measure of the amount of pollutant received by the indicator. U.S. Pat. No. 5,659,296 describe a contemporary but still cumbersome system using electronic device attached to the side of the respirator. Air passed through the sorbent material was constantly sampled and processed to give an active indication—with visual, audio, tactile response to the concentration signal. The signaling rate of the indicator varied as a function of target species concentration. The drawback of described system is again placement of the proposed sensors directly behind the respirator cartridge which is after 100% depletion to allow time for safety replacement of the cartridge. The drawbacks of most proposed systems are also high energy consumption and cumbersome equipment.
Conventional solutions suffer from many drawbacks such as:
The described electronic or optic-electronic devices are complicated and bulky, difficult to maintain and even to manufacture and use at contemporary level of technology of sensors.                The ultimate cost is so high that the cost eradicates the purpose of their use as money saving unit as compared to just replacing canisters and cartridges on a schedules for timely change. In order to provide secure buffer capacity of 20-25% an additional portion of sorbent is intended to be used after the sensing element.        Build-in cartridge/canister electronic sensor should be capable of withstanding any chemical pretreatments with reagents of the sorption media. The cartridge/canister should be physically shared in two portions: first portion of the cartridge/canister should contain approximately 75-80% of the sorbent, then sensing element, then second buffering portion of the canister having 20-25% of the sorbent, respectively portion of total capacity. Cartridges with build-in sensors have comparably high cost which will completely eliminate one main purpose of the sensor—low cost of indication of depletion of the cartridge to deliver a high safety level.        
Thus, there is a need for a system for secure and effective end-of-service life of the indication allowing buffer time and sorptive capacity after less than complete depletion of the sorbent media. There is a further need for a light weight, more easily manufactured, and uncomplicated design for a system and device for end of service life indication.
There is a still further need for a end of service life indication system or method capable of estimating the remaining cartridge life substantially during real time and that allows communication between the user and the system capable of generating warning signals to the user when desired.